ANALYSIS OF TORSIONAL SPECTRA OF MOLECULES WITH TWO $C_{3v}$ INTERNAL ROTORS. cis- AND trans-2 Butene

Author Institution:The low-frequency Raman and far infrared spectra of gaseous cis- and trans-2-butene have been recorded from 70 to $450 cm^{-1}$. Considerable torsional data have been obtained for the trans-2-butene, molecule with the $A_{u}$ torsional fundamental being observed at $163.6 cm^{-1}$ in the infrared spectrum. The overtone of the B fundamental was observed in the Raman spectrum at $432 cm^{-1}$. The potential function based on a semi-rigid model and the effective barrier was found to be $703 cm^{-1}$ (2.04 kcal/mole). The cosine-cosine coupling term, $V_{33}$, was found to be zoro whereas the sine-sine coupling term, $V_{33}$ has a value of -$48 cm^{-1}$ (-0.14 kcal/mole) and $V_{60} =V_{06} = -4 cm^{-1}$ (-0.01 kcal/mole). For the cis-2- butane molecule only the $B_{2}$ torsional mode was observed at $101.0 cm^{-1}$ which gives an effective barrier of $250 cm^{-1}$ (0.87 kcal/mole). These data are compared to the corresponding quantities obtained earlier by other methods